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The Crew Return Vehicle (CRV), sometimes referred to as the Assured Crew Return Vehicle (ACRV), is the proposed lifeboat or escape module for the International Space Station (ISS). A number of different vehicles and designs have been considered over the past two decades – with several flying as developmental test prototypes – but no one single design has been built as the dedicated CRV. In the original space station design, emergencies were intended to be dealt with by having a "safe area" on the station that the crew could evacuate to, pending a rescue from a U.S. Space Shuttle. However, the 1986 Space Shuttle ''Challenger'' disaster and the subsequent grounding of the shuttle fleet caused station planners to rethink this concept.〔(NASA ACRV history from Astronautix.com )〕 Planners foresaw the need for a CRV to address three specific scenarios: * Crew return if a space shuttle or Soyuz capsule was unavailable; * An escape vehicle from a major time-critical space station emergency; * Full or partial crew return in case of a medical emergency. == Medical considerations == The ISS is equipped with a Health Maintenance Facility (HMF) to handle a certain level of medical situations, which are broken into three main classifications: * Class I: non-life-threatening illnesses and injuries (headache, lacerations). * Class II: moderate to severe, possibly life-threatening (appendicitis, kidney stones). * Class III: severe, incapacitating, life-threatening (major trauma, toxic exposure). However, the HMF is not designed to have general surgical capability, so a means of evacuating a crew member in case of a medical situation that is beyond the HMF's capabilities is essential.〔 A number of studies have attempted to assess the medical risks for long-term space station habitation, but the results are inconclusive, as epidemiological data is lacking. It is, however, understood that longer periods in space increase the risk of serious problems. The closest estimates show an illness/injury rate of 1:3 per year, with 1% estimated to require emergency evacuation by means of a CRV. For an eight-person ISS crew, this results in an expected need for a CRV flight once every 4 to 12 years. These estimates have been partially corroborated by experiences on board the Soviet Union's ''Mir'' space station. In the 1980s, the Soviets had at least three incidents where cosmonauts had to be returned under urgent medical conditions.〔 Because of its potential use as a medical evacuation method, the CRV design was required to address a number of issues that are not factors for a standard crewed space vehicle. Foremost of these are the ''g''-loadings as influenced by reentry profiles and deceleration/landing methods upon patients with hemorrhagic shock issues. Patient security issues are more critical for injured astronauts than for uninjured personnel. Additionally, depending on the nature of the injury, it may be unlikely that the patient could be placed in an environmentally contained space suit or minicapsule, therefore the CRV needs to have the capability to provide a "shirt sleeve" environment. The ability to address air purity issues is included in this requirement, as air purity is especially critical in medical as well as toxic exposure situations.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Crew Return Vehicle」の詳細全文を読む スポンサード リンク
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